4X6 Magnetifm, Mineralogy, &c. 



MAGNETISM. 



Wenzel has proved that cobalt is fufceptible of magnetic 

 attraction, and has magnetic poles. Klaproth has proved 

 that the pureft nickel, that even of the Chrifoprafus, is alfo 

 fufceptible of the fame attraction, and has magnetic poles. 

 The ferpentine of Humboldt has magnetic poles, but does 

 not attract iron. The cafe is the fame with feveral forts of 

 lava. Here then are bodies which have polarity, without 

 attracting iron. Are there bodies which act upon iroifi 

 without having polarity ? Tralles, a geometrician of Berne, 

 has taken very fraall fragments of Humboldt's ferpentine, 

 which had very perceptible poles, and having placed them 

 clofe to very ftrong magnets, the poles of which were op- 

 pofite to thofe of the ferpentine, the poles of the ferpentine 

 became inverted. 



MINERALOGY. 



Several mineralogifts think that the metallic veins in 

 mines diminifh always in thicknefs the deeper they pro- 

 ceed ; fo that thefe veins refemble a kind of wedge, the 

 bafe of which is directed towards the furface of the earth, 

 and the point towards the centre. But this is not precifely 

 the cafe. Several veins appear indeed to be of that form ; 

 but there are many others, the form of which is quite the 

 rcverfe. Humboldt fays that the vein of Kuhchacht at 

 Freyberg, which contains argentiferous galena, grows 

 broader, inftead of becoming narrower, the deeper it goes ; 

 and yet it is one of the deepeft worked, as it proceeds to 

 the depth of feveral hundreds of fathoms. Thofe of 

 Goldcronach in Franconia, which contain arfenical and 

 auriferous pyrites, are much broader at a certain depth than 

 at the furface. 



COLD PRODUCED BY COMPRESSED AIR. 



Thofe machines employed for ftrongly compreffing at- 

 oaofpheric air are well known, Profeflbr Pictet of Geneva 



fey s, 



